Multicomponent aliphatic polyester blend fibers

ABSTRACT

The present invention provides multicomponent thermoplastic fibers that are biodegradable and that are capable of forming strong bonds in air bonding processes. In various embodiments, the multicomponent fibers can include a first polymer component that includes a first aliphatic polyester, and a second polymer component also including an aliphatic polyester, wherein the first polymer component comprises at least a portion of an exposed surface of the multicomponent fiber. The first polymer component can be a fully amorphous polylactic acid and the second polymer component can be a semicrystalline polylactic acid. The multicomponent fiber can have cross-sectional area comprising the first polymer component and the second polymer component in about a 1:1 ratio, wherein the first polymer component and the second polymer component are configured in a sheath/core arrangement.

FIELD OF INVENTION

The present disclosure relates to a multicomponent thermoplastic fiber.In particular, the fiber can exhibit useful thermal-bondingcharacteristics, such as during thermal-bonding processes, includingthermal bonding processes that do not require application of pressure.

BACKGROUND

Synthetic fibers are widely used in a number of diverse applications toprovide stronger, thinner, and lighter weight products. Syntheticthermoplastic fibers are typically heat adhesive (thermobondable) andthus are particularly attractive for the manufacture of nonwovenfabrics, either alone or in combination with other fibers (such ascotton, wool, and wood pulp). Nonwoven fabrics, in turn, are widely usedas components of a variety of articles, including without limitationabsorbent personal care products, such as diapers, incontinence pads,feminine hygiene products, and the like; medical products, such assurgical drapes, sterile wraps, and the like; filtration devices;interlinings; wipes; furniture and bedding construction; apparel;insulation; and others.

Conventional synthetic thermoplastic fibers, however, do not naturallydegrade, thus creating problems associated with the disposal of productscontaining such fibers. In particular, recycling articles containing ablend of natural and conventional synthetic fibers is generally not costeffective, but the disposal of these articles in landfills generatessignificant amounts of non-degradable waste. As landfills reach theircapacity, the demand has increased for the incorporation of moredegradable components in disposable products, as well as the design ofproducts that can be disposed of by means other than by incorporationinto solid waste disposal facilities.

To address concern over the issue of solid waste disposal, biodegradablepolymers are increasingly used as a replacement for conventionalsynthetic polymers. Biodegradable polymers of interest includewater-soluble polymers such as polyvinyl alcohol; naturally synthesizedpolymers such as sodium alginate and microbial polyesters; hydrolyzablealiphatic polyester and polyurethane polymers; and the like. Syntheticbiodegradable aliphatic polyesters include polyglycolide and polylacticacid polymers. See, for example, U.S. Pat. Nos. 5,166,231; 5,506,041;5,759,569; 5,171,309; 6,177,193; 6,441,267; 6,953,622; and 7,338,877,each of which is herein incorporated by reference in its entirety.

Of particular interest is the use of lactic acid to manufacturebiodegradable resin. Polylactic acid (hereinafter “PLA”) was initiallyintroduced as a biodegradable polymer for medical products. U.S. Pat.Nos. 5,142,023 and 5,807,973 to Gruber et al., each of which is hereinincorporated by reference in its entirety, disclose processes by which anonmedical grade of polylactic acid may be produced and utilized innonwoven fabrics. Examples of biodegradable fibers comprised entirely ofpolylactic acid polymers and/or copolymers are found in U.S. Pat. Nos.5,010,145 and 5,760,144, each of which is herein incorporated byreference in its entirety. See also U.S. Pat. Nos. 5,698,322 and5,593,778 (directed to bicomponent fibers which include polylactic acidcomponents), each of which is herein incorporated by reference in itsentirety.

The successful inclusion of biodegradable materials in disposableabsorbent products provides several avenues by which these products maybe discarded once their useful life has ended. Primarily, these articlesmay be easily and efficiently disposed of by composting. Alternatively,the disposable product may be easily and efficiently disposed of to aliquid sewage system wherein the disposable absorbent product is capableof being degraded.

Although biodegradable fibers are known, problems have been encounteredwith their use. For example, the known biodegradable fibers may bondwhen melted under pressure (calendar-bonding), but such fibers may notform a strong bond in other processes, such as an air-bonding process.Furthermore, many conventional binder fibers exhibit shrinkage atair-bonding temperatures since the fiber cannot be heatset at or abovethe temperature at which the binder component will soften or flow, yetin bonding, the fiber must be exposed to temperatures high enough toachieve the desired melt flow characteristics of the binder component.Therefore, it is desirable to provide an entirely biodegradable fiberthat is capable of forming a strong bond in an air-bonding process.

SUMMARY OF THE INVENTION

The present invention provides multicomponent thermoplastic fibers thatare biodegradable and that are useful in thermal bonding processes,particularly air bonding processes. The multicomponent fiber can beselected from the group consisting of continuous filaments, staplefibers, spunbond filaments, and meltblown fibers. In variousembodiments, the multicomponent fibers comprise a first polymercomponent comprising a first aliphatic polyester, and a second polymercomponent also comprising an aliphatic polyester, wherein the firstpolymer component comprises at least a portion of an exposed surface ofthe multicomponent fiber. In some embodiments, about 5% or greater,about 15% or greater, about 25% or greater, about 50% or greater, orabout 75% or greater of the exposed multicomponent fiber surface can bedefined by the first polymer component. In a preferred embodiment, theentire exposed surface of the multicomponent fiber can be defined by thefirst polymer component. Furthermore, the multicomponent fiber can havea cross-sectional area comprising the first polymer component and thesecond polymer component in a ratio of about 1:9 to about 9:1, or in aratio of about 1:3 to about 3:1. In some embodiments, the ratio of thecross-sectional area is about 1:1.

In various embodiments, the first polymer component is polylactic acid.In some embodiments, the first polymer component comprises a fullyamorphous polylactic acid, wherein the D-isomer content of the amorphouspolylactic acid is about 5% or greater, or about 8% or greater. Inaddition, in various embodiments, the first polymer component can have amelt flow index of about 30 or greater when evaluated according to meltflow test ASTM D1238 at a temperature of 210° C. and using a 2160 gbasis weight. In various embodiments, the melt flow index of the firstpolymer component is about 45 or greater, or about 60 or greater. Insome embodiments, the first polymer component can further comprise anadditive adapted to one or both of increase the melt flow rate of thefirst polymer component and reduce the viscosity of the first polymercomponent at a target bonding temperature. Thereby, the additive mayreduce the temperature at which satisfactory bonding can occur. Thebonding temperature can be defined as the temperature at which the firstpolymer component softens or flows sufficiently to enable bondingbetween adjacent fibers, and wherein the second polymer component doesnot soften, flow or melt, such that the fibrous shape of themulticomponent fiber is maintained. The additive can be present in anamount sufficient to reduce the bonding temperature of multicomponentfiber at which satisfactory bonding occurs by about 10° C. or more. Thiscan be advantageous because with conventional air bonding, thetemperature required for satisfactory bonding of the sheath componentcan be above the temperature at which the core component either softensor melts or shrinks to an unacceptable degree. Therefore, reducing thebonding temperature can provide energy savings, increased line speed,and make air bonding a practical option for binder fibers disclosedherein, whereas conventional fibers are limited to use in a pressurebonding process such as calendar bonding or point bonding, for example.

In various embodiments of the multicomponent fiber, the first polymercomponent is defined by a first molecular weight, and the second polymercomponent is defined by a second molecular weight. Furthermore, thefirst polymer component can comprise an additive in an amount sufficientto reduce the first molecular weight to a first reduced molecularweight. In various embodiments, the first reduced molecular weight isless than the first molecular weight by about 10% or more. For example,the ratio of the first reduced molecular weight to the first molecularweight can be about 0.9 or less, or about 0.85 or less. Additionally,the weight ratio of the first polymer component and the second polymercomponent can vary. For example, in some embodiments, the first polymercomponent can have a molecular weight that is about 90% or less, about85% or less, or about 80% or less of the molecular weight of the secondpolymer component. In some embodiments, the first polymer component caninclude a molecular weight reducing additive. In various embodiments,the first polymer component comprises about 0.5% to about 8.0% by weightof the molecular weight reducing additive. In further embodiments,exemplary molecular weight reducing additives can be selected from thegroup consisting of pentaerythritol, water, sodium hydroxide, hydratedalumina trihydrate, ethylene glycol, and combinations thereof.

In various embodiments, the second polymer component is polylactic acid.In some embodiments, the second polymer component comprises asemicrystalline polylactic acid, wherein the D-isomer content of thesemicrystalline polylactic acid is about 2% or less, about 1% or less,or about 0.6% or less. In some embodiments, the second polymer componentcomprises a blend of a first semicrystalline polylactic acid, whereinthe D-isomer content of the first semicrystalline polylactic acid isabout 1.2% or less, and a second semicrystalline polylactic acid,wherein the D-isomer content of the second semicrystalline polylacticacid is about 2% or less. Such blend can be at a ratio of about 10:90 toabout 90:10 or about 25:75 to about 75:25. In various embodiments, thesecond polymer component has a melt temperature of about 160° C. orgreater.

The present invention also overcomes known problems in the art relatedto acceptable bonding with a binder fiber in an air-bonding process. Inparticular, the presently disclosed fibers can be characterized by beingresistant to shrinkage during heating. In some embodiments, the fiberscan be defined by a desirable heat shrinkage value. Specifically, afiber according to the present disclosure can be defined by a heatshrinkage value of less than 20%, preferably less than 15%, and mostpreferably less than about 10% when subjected to thermal air bondingconditions. Particularly, the heat shrinkage values can be evaluatedunder conditions of being exposed to air at a temperature of about 130°C. for a time of approximately 5 minutes. Shrinkage can be evaluated atvarious temperatures and lengths of time depending on the target bondingtemperature of an embodiment of the multicomponent fiber.

Furthermore, the present disclosure can provide a fabric comprising aplurality of thermally bonded multicomponent fibers as described herein.In certain embodiments, such fabrics can exhibit a tensile strength ofabout 500 grams force to about 4500 grams force or greater per gram offabric weight. In further embodiments, a heat bonded nonwoven fabricaccording to the disclosure can exhibit a tensile strength about 150grams force or greater for a fabric sample having a length and width ofabout 1.5 inches and about 2 inches, respectively, and having a weightof about 0.1 to about 0.3 grams.

In particular, the present multicomponent fiber can be adapted to imparta bonded web strength of about 150 grams force or greater for a bondednonwoven comprising the multicomponent fiber as the sole bonding agent,wherein the bonded web strength is evaluated in relation to a cardednonwoven web of 75% PLA 6202D fiber and 25% by weight of themulticomponent fiber, the web having a length of about 1.5 inches, awidth of about 2 inches, and a weight of about 0.1 to about 0.3 grams,and the web being air bonded with a 12 second residence time in abonding oven at a temperature of 130° C.

In various embodiments, a method of forming a fabric comprises providinga plurality of multicomponent fibers each with an exposed surface,wherein each multicomponent fiber comprises a first polymer componentand a second polymer component, and wherein the first polymer componentforms at least a portion of an exposed surface of each multicomponentfiber; and thermal air bonding the plurality of multicomponent fibers.In some embodiments, the bonding can be carried out at a temperature ofabout 80° C. to about 150° C. The second polymer component particularlycan have a melting temperature that is greater than the bondingtemperature.

The fibers disclosed herein further can be used in the manufacture offurther materials. For example, the present disclosure also encompassesspun yarns comprising the present fibers. In further, non-limitingexamples, materials that can comprise the present fibers include plugs,tows, waddings, ropes, cords, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 is a transverse cross sectional view of an exemplary sheath/coremulticomponent fiber of the invention;

FIG. 2 is a transverse cross sectional view of a second exemplarysheath/core multicomponent fiber of the invention;

FIG. 3 is a transverse cross sectional view of an exemplary “islands inthe sea” multicomponent fiber of the invention;

FIG. 4 is a transverse cross sectional view of an exemplary side-by-sidemulticomponent fiber of the invention;

FIG. 5 is a transverse cross sectional view of an exemplary pie-wedgemulticomponent fiber of the invention; and

FIG. 6 is a transverse cross sectional view of an exemplary multi-lobalmulticomponent fiber of the invention.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein; rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the invention to thoseskilled in the art. As used in this specification and the claims, thesingular forms “a,” “an,” and “the” include plural referents unless thecontext clearly dictates otherwise. Reference to “dry weight percent” or“dry weight basis” refers to weight on the basis of dry ingredients(i.e., all ingredients except water).

The present disclosure provides a multicomponent thermoplastic fiberthat is biodegradable and that forms strong bonds in thermal bondingprocesses. The multicomponent fiber can comprise a first polymercomponent comprising a first aliphatic polyester and a second polymercomponent comprising a second aliphatic polyester, wherein the firstpolymer component comprises at least a portion of an exposed surface ofthe multicomponent fiber. In some embodiments as used herein, an exposedsurface can refer to at least a portion of a circumference of across-sectional area of the multicomponent fiber. In furtherembodiments, an exposed surface can comprise any area of the fibersurface that is exposed to ambient surroundings.

The term “fiber” as used herein means both fibers of finite length, suchas conventional staple fibers, as well as substantially continuousstructures, such as continuous filaments, unless otherwise indicated.The fibers of the invention can be hollow or non-hollow fibers, andfurther can have a substantially round or circular cross section ornon-circular cross sections (for example, oval, rectangular,multi-lobed, and the like).

As used herein, the term “multicomponent fibers” includes staple andcontinuous fibers prepared from two or more polymers present in discretestructured domains in the fiber, as opposed to blends where the domainstend to be dispersed, random or unstructured. For purposes ofillustration only, the present subject matter is generally described interms of an exemplary bicomponent fiber comprising two polymercomponents. However, it should be understood that the scope of thepresent invention is meant to include fibers with two or more structuredcomponents and is not limited to the exemplary bicomponent fibersdescribed below. Although the invention is not limited to twocomponents, the terms first component and second component are usedthroughout for the ease of describing the invention.

In general, the polymer components are arranged in substantiallyconstantly positioned distinct zones across the cross section of themulticomponent fiber and extend continuously along the length of themulticomponent fiber. Both the shape of the fiber and the configurationof the components therein will depend upon the equipment that is used inthe preparation of the fiber, the process conditions, and the meltviscosities of the various components. A wide variety of fiberconfigurations are possible in the present invention. The cross sectionof the multicomponent fiber can particularly be circular, since theequipment typically used in the production of multicomponent syntheticfibers often produces fibers with a substantially circular crosssection; however, other cross sections are encompassed. Theconfiguration of the first and second components in a fiber of circularcross section can be either concentric or eccentric, the latterconfiguration sometimes being known as a “modified side-by-side” or an“eccentric” multicomponent fiber.

FIG. 1 is a cross-sectional view of an exemplary multicomponent fiber ofthe present invention, designated generally as 10. Multicomponent fiber10 is a sheath/core fiber that includes at least two structured polymercomponents: (i) an outer sheath component comprising a first polymercomponent 2; and (ii) an inner core component comprising a secondpolymer component 2.

The core (formed of the second polymer component 4) can be concentric,as illustrated in FIG. 1. Alternatively, the core can be eccentric, asshown in FIG. 2, which illustrates an eccentric sheath/core fiber 10.The eccentric sheath/core fiber 10 is substantially the same as theembodiment of FIG. 1, except the core (formed of the second polymercomponent 4) is eccentrically located within the outer sheath (formed ofthe first polymer component 2).

A concentric configuration is characterized by the sheath componenthaving a substantially uniform thickness so that the core component liesapproximately in the center of the fiber, such as illustrated in FIG. 1.This is in contrast to an eccentric configuration, such as illustratedin FIG. 2, in which the thickness of the sheath component varies, andthe core component therefore does not lie in the center of the fiber.Concentric sheath/core fibers can be defined as fibers in which thecenter of the core component is biased by no more than about 0 to about20 percent, preferably no more than about 0 to about 10 percent, basedon the diameter of the sheath/core multicomponent fiber, from the centerof the sheath component.

Other structured fiber configurations as known in the art can also beused. For example, FIG. 3 illustrates another advantageous embodiment ofthe invention in which the multicomponent fiber 10 of the invention is a“matrix” or “islands in a sea” type fiber having a plurality of inner,or “island,” polymer components surrounded by an outer matrix, or “sea,”polymer component. The island components can be substantially uniformlyarranged within the matrix of the sea component, such as illustrated inFIG. 3. Alternatively, the island components can be randomly distributedwithin the sea matrix. In various embodiments, the sea polymer componentcomprises the first polymer component 2. In various embodiments, theisland polymer components comprise the second polymer component 4.

FIG. 4 illustrates yet another embodiment of the invention; namely, aside-by-side multicomponent fiber 10 wherein the first polymer component2 and the second polymer component 4 are arranged in a side-by-siderelationship. FIG. 5 illustrates an embodiment of the invention whereinthe multicomponent fiber 10 is configured in a pie-wedge arrangement,wherein the first polymer component 2 and the second polymer component 4are arranged as alternating wedges.

The multicomponent fibers of the present invention can also includemultilobal fibers having three or more arms or lobes extending outwardlyfrom a central portion thereof. FIG. 6 is a cross sectional view of anexemplary multilobal fiber 10 of the invention. Fiber 10 includes acentral core formed of the second polymer component 4 and arms or lobesformed of the first polymer component 2 and extending outwardlytherefrom.

Various embodiments of the multicomponent fiber have a cross-sectionalarea comprising the first polymer component and the second polymercomponent in about a 1:9 to about a 9:1 ratio; or about a 1:3 to about a3:1 ratio. In some embodiments, the multicomponent fiber has across-sectional area comprising the first polymer component and thesecond polymer component in about a 1.5:2.5 to about a 2.5:1.5 ratio. Ina preferred embodiment, the multicomponent fiber has a cross-sectionalarea comprising the first polymer component and the second polymercomponent in about a 1:1 ratio. In various embodiments, the firstpolymer component and the second polymer component can be present in amass ratio of about 90:10 to about 10:90.

In various embodiments of a multicomponent fiber described herein, thefirst polymer component can form at least a portion of the exposed outersurface of the multicomponent fiber. In some embodiments, about 5% orgreater, about 15% or greater, about 25% or greater, about 50% orgreater, or about 75% or greater of the exposed multicomponent fibersurface can be defined by the first polymer component. In a preferredembodiment, the entire exposed surface of the multicomponent fiber canbe defined by the first polymer component.

In various embodiments of the multicomponent fiber described herein, thepolymer components of the multicomponent fiber can be formed of the sameor different polymers. As used herein, the “same” polymer refers topolymer components having an identical or similar chemical formula;however, each polymer component can differ with respect to their abilityto flow at a target bonding temperature. The ability of a polymercomponent to flow at a temperature is related to crystallinity,molecular weight, and the possible presence of plasticizers. The firstpolymer component and the second polymer component can each be analiphatic polyester. Examples of aliphatic polyesters which may beuseful in the present invention include, without limitation, fiberforming polymers formed from (1) a combination of glycol (e.g.,ethylene, glycol, propylene glycol, butylene glycol, hexanediol,octanediol or decanediol) or an oligomer of ethylene glycol (e.g.,diethylene glycol or triethylene glycol) with an aliphatic dicarboxylicacid (e.g., succinic acid, adipic acid, hexanedicarboxylic acid ordecaneolicarboxylic acid) or (2) the self condensation of hydroxycarboxylic acids other than polylactic acid, such as polyhydroxybutyrate, polyethylene adipate, polybutylene adipate, polyhexaneadipate, and copolymers containing them. Examples of aliphaticpolyesters include, but are not limited to, polyglycolide orpolyglycolic acid (PGA), polylactide or polylactic acid (PLA),polycaprolactone (PCL), polyethylene adipate (PEA), polyhydroxyalkonoate(PHA), polyhydroxybutyrate (PHB),poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), andpolylactide-co-glycolide.

Aliphatic polyesters can be particularly useful because of thebiodegradable nature thereof. In addition to biodegradability, aliphaticpolyesters, particularly polylactic acid, can impart other desirableproperties to the fibers of the invention. For example, the fibers ofthe invention which include polylactic acid (or a further aliphaticpolyester) as a component can exhibit improved hydrophilic properties,improved flame retardant capabilities, or can be dyed to deeper andbrighter shades as compared to fibers including polyethyleneterephthalate or polyamides traditionally employed in the core ofbicomponent binder fibers.

In various embodiments, the first polymer component comprises a firstaliphatic polyester and the second polymer component comprises a secondaliphatic polyester. However, in embodiments where the first polymercomponent and the second polymer component comprise the same type ofaliphatic polyester, then the first aliphatic polyester and the secondaliphatic polyester can each be defined by at least one distinguishingcharacteristic. In a preferred embodiment, the first aliphatic polyesterand the second aliphatic polyester are both polylactic acid, wherein thefirst PLA polymer component is defined by at least one distinguishingcharacteristic related to the ability of the polymer component to flowand form a strong bond at the target bonding temperature.

Polylactic acid polymers useful according to the present disclosure canbe prepared by either the polymerization of lactic acid or lactide. PLAand methods of making thereof are disclosed in U.S. Pat. Nos. 5,698,322;5,142,023; 5,760,144; 5,593,778; 5,807,973; and 5,010,145, and theentire disclosure of each is hereby incorporated by reference.

Advantageously, PLA polymers useful according to the present disclosureexhibit residual monomer percents effective for the first polymercomponent and the second polymer to exhibit desirable melt strength,fiber mechanical strength, and fiber spinning properties. As usedherein, “residual monomer percent” refers to the amount of lactic acidor lactide monomer that is unreacted yet which remains entrapped withinthe structure of the entangled PLA polymer chain. In general, if theresidual monomer percent of a PLA polymer in a component is too high,the component may be difficult to process due to inconsistent processingproperties caused by a large amount of monomer vapor being releasedduring processing that causes variations in extrusion pressures.However, a minor amount of residual monomer in a PLA polymer in acomponent may be beneficial due to such residual monomer functioning asa plasticizer during a spinning process. Thus, a PLA polymer componentgenerally exhibits a residual monomer percent that is less than about 15percent, preferably less than about 10 percent, and more preferably lessthan about 7 percent.

Aliphatic polyesters useful in the present disclosure can be defined bydifferent characteristics or properties. For example, with reference toPLA, lactic acid and lactide are known to be asymmetrical molecules,having two optical isomers referred to, respectively as the levorotatory(hereinafter referred to as “L”) enantiomer and the dextrorotatory(hereinafter referred to as “D”) enantiomer, As a result, bypolymerizing a particular enantiomer or by using a mixture of the twoenantiomers, it is possible to prepare polymers that are chemicallysimilar yet which have significantly differing properties. Inparticular, it has been found that by modifying the stereochemistry of apolylactic acid polymer, it is possible to control the meltingcharacteristics of the polymer.

Crystallinity is another property that can be used to define aliphaticpolyesters. The degree of crystallinity of a PLA polymer, for example,is based on the regularity of the polymer backbone and its ability toline up with similarly shaped sections of itself or other chains. Ifeven a relatively small amount of D-enantiomer (of either lactic acid orlactide), such as about 3 to about 4 weight percent, is copolymerizedwith L-enantiomer (of either lactic acid or lactide), the polymerbackbone generally becomes irregularly shaped enough that it cannot lineup and orient itself with other backbone segments of pure L-enantiomerpolymer, thus reducing the crystallinity of the polymer, which in turncan decrease the bonding temperature at which the polymer formssatisfactory bonds below a defined value. In various embodiments, theinclusion of a nucleating agent can increase the crystallinity of apolymer component.

In various embodiments, a melt flow index measurement is used to definean aliphatic polyester. Tests known in the art can be used to measurethe melt flow index of a polymer component. For example, melt flow testASTM D1238 can be used to determine the melt flow index of a polymercomponent.

Additionally, aliphatic polyesters can be defined by their molecularweight. Molecular weight can refer to the length of each polymer chain.Thus, the first and second polymer components may have the same ordifferent molecular weights. While a difference in molecular weight canbe inherent to the polymer grade, in various embodiments, a polymercomponent can comprise an additive which causes a reduction of thepolymer's molecular weight. In various embodiments, the additive causesthe reduction in the polymer's molecular weight during extrusion. Invarious embodiments, extrusion refers only to the fiber extrusionprocess (i.e., the additive is added immediately prior to fiberextrusion,) In some embodiments, extrusion refers to a first extrusionwherein the additive can be added into the polymer component to form acompound that is later extruded in a second extrusion to form a fiber.Two or more extrusions can cause a larger reduction in molecular weightthan a single extrusion. In various embodiments, the additive can causea reduction in the polymer component's molecular weight of about 5% orgreater, about 10% or greater, or about 15% or greater. Accordingly, insome embodiments, the molecular weights of the first and second polymercomponents can be substantially identical, and the additive can beutilized to reduce the molecular weight of the first polymer componentto achieve a desired molecular weight ratio as otherwise describedherein. In various embodiments, the molecular weight ratio of the firstpolymer after extrusion as compared to before extrusion is less than 1.0or is about 0.95 or less, about 0.9 or less, or about 0.85 or less.

A non-limiting example of an additive that can be utilized according tothe present disclosure is pentaerythritol, which can be added to apolymer component prior to or during extrusion. Pentaerythritol reducesthe molecular weight of condensation polymers such as esters byhydrolysis. In preferred embodiments, the first polymer component can beblended with about 0.5% to about 8% by weight or about 1.5% to about4.5% by weight of pentaerythritol prior to or during extrusion. Other,non-limiting examples of additives that can be included in a polymercomponent to reduce the molecular weight of the polymer componentinclude water, sodium hydroxide, hydrated alumina trihydrate, ethyleneglycol, and the like.

In some embodiments, an additive can be utilized that improves bondingperformance of a multicomponent fiber without necessarily reducing themolecular weight of a polymer component. For example, plasticizers suchas an aliphatic diester and/or a polyhydroxyalkanoate (“PHA”) can beincluded in a PLA polymer component. Such additives can be blended witha polymer component prior to or during extrusion, as described above.

As further described herein, the fibers of the present invention can beparticularly useful as a binder fiber or can be adapted for improvedbonding, particularly in bonding methods such as air bonding.Accordingly, in various embodiments it is desirable for the secondpolymer component to have a melting temperature that is greater than asoftening temperature of the first polymer component. The second polymercomponent can be selected to provide strength or rigidity to the fiberand, thus, to nonwoven structures comprising the multicomponent fiber.Strength or rigidity of the fiber is generally achieved by selecting asecond polymer component having a thermal melting temperature greaterthan the softening temperature of the first polymer component. Thus,when the multicomponent fiber is subjected to an appropriate bondingtemperature, typically greater than the softening temperature of thefirst polymer component but less than the melting temperature of thesecond polymer component, the first polymer component will soften andpreferably flow while the second polymer component will generallymaintain its rigid form. This is especially desirable in the preferredsheath/core arrangement described above. Furthermore, by the secondpolymer component not melting at the target bonding temperature, thefibrous shape of the multicomponent fiber can be maintained.

A PLA binder fiber undergoing an air-bonding process can suffer fromheat shrinkage since the fiber cannot be heatset at or above atemperature at which the binder component will soften or flow, yet inbonding, the fiber must be exposed to temperatures high enough toachieve the desired melt flow characteristics of the binder component.The heat shrinkage mainly occurs due to the thermally-induced chainrelaxation of the polymer segments that are present in the amorphousphase. At bonding temperatures then, significant heat shrinkage istypically observed. This is a particular problem with PLA because itsshrinkage force is known in the art to be relatively high. Thus, whensuch fiber is utilized in forming a heat bonded fabric, the shrinkingbinder fiber is more likely to cause holes or non-uniformities in thefabric as it shrinks. According to the present invention, however, usinga PLA with a relatively high L-isomer purity in the core of amulticomponent fiber can significantly lower shrinkage of the fiber.

Accordingly, a polymer component useful in the present invention can bedefined by a D-isomer content, as discussed above. Specifically, theL-isomer purity of a PLA polymer component can affect the meltingcharacteristics of the polymer. The melting characteristics of therespective polymers thus can be defined by the isomeric content of thepolymeric components. In various embodiments, the isomeric purity of thesecond polymer component is higher than the isomeric purity of the firstpolymer component. For example, a first polymer component of themulticomponent fiber described herein can be a fiber component thatsoftens or flows at a target bonding temperature while a second polymercomponent does not substantially soften, flow, or melt at the sametarget bonding temperature. Therefore, the first polymer component cancomprise a fully amorphous PLA with a bonding temperature that is at orbelow a defined value. In various embodiments, the first polymercomponent can comprise polylactic acid defined by a D-isomer content ofabout 2% or more, about 3% or more, about 4% or more, or about 5% ormore. In a preferred embodiment, the first polymer sheath component isan amorphous PLA that can be modified such that the first polymer sheathcomponent softens or flows more readily at the target bondingtemperature. In some embodiments, a semicrystalline PLA (i.e. with a Dcontent below about 5%) can be a useful binder sheath in combinationwith a PLA core polymer of high L-isomer purity. For example, anon-bonding (second) polymer component comprising a roughly equal blendof relatively pure PLA with relatively pure PDLA (conventionally knownas a “stereocomplex”) has a sufficiently high melt temperature such thata semicrystalline PLA with a D-content of about 0.1% to about 5% can beused as the first (bonding) polymer component.

In various embodiments the second polymer component comprises asemicrystalline PLA. In some embodiments, the second polymer componentcomprises a PLA stereocomplex. In some embodiments, the second PLApolymer component preferably comprises only a small amount of D-isomersuch that the melting point of the second polymer component is notdecreased below a defined value. Moreover, the second polymer component(e.g., a core polymer component) can comprise PLA with a D-isomercontent of about 2.0% or less, about 1.2% or less, about 1.0% or less,about 0.8% or less, or about 0.6% or less. As described, D-isomercontent of a core component polymer can beneficially reduce heatshrinkage of the fiber. Accordingly, in light of the foregoing, D- andL-isomer content of the first and second polymer components can becombined such that a fiber formed therewith exhibits a heat shrinkagevalue of less than 20%, preferably less than 15% and most preferablyless than about 10% when exposed to air at a temperature of about 130°C. for a time of approximately 5 mins. The inclusion of a nucleatingagent can also increase the crystallinity of the second polymercomponent.

Additionally, a polymer component can be defined by a meltingtemperature, particularly relative melting temperatures. In someembodiments, the second polymer component has a melt temperature ofabout 160° C. or greater, although further melt temperature points canbe utilized depending upon the desired processing conditions.Preferably, the first polymer component has a bonding temperature thatis significantly below the melt temperature of the second polymercomponent such that softening or flowing of the first polymer componentoccurs at a temperature that does not significantly soften or melt thesecond polymer component. If desired, additional additives can be addedto the polymer components in order to differentiate the meltingcharacteristics of two PLA components. In some embodiments, the firstpolymer component comprises an additive suitable to reduce the bondingtemperature of the first polymer component.

As discussed above, melt flow index is another property that can be usedto distinguish between two PLA polymer components. In variousembodiments first polymer component has a melt flow index of about 30 orgreater when tested according to melt flow test ASTM D1238 at atemperature of 210° C. and using a 2160 g basis weight. In anembodiment, the first polymer component has a melt flow index of about45 or greater under the same test conditions. In a preferred embodiment,the first polymer component has a melt flow index of about 60 or greaterunder the same test conditions.

Each of the thermobondable first polymer component and second polymercomponent can optionally include other components not adverselyaffecting the desired properties thereof. Exemplary materials whichcould be used as additional components would include, withoutlimitation, pigments, antioxidants, stabilizers, surfactants, waxes,flow promoters, solid solvents, particulates, and other materials addedto enhance processability of the first and the second components. Forexample, a stabilizing agent may be added to the biodegradable polymerto reduce thermal degradation which might otherwise occur during thepolylactic acid spinning process. The use of such stabilizing agents isdisclosed in U.S. Pat. No. 5,807,973, hereby incorporated in itsentirety by reference. Further, additives which enhance thebiodegradability of the polylactic acid may optionally be included, asdisclosed in U.S. Pat. No. 5,760,144, previously incorporated byreference. These and other additives can be used in conventionalamounts.

If desired, a fiber according to the present disclosure can comprise oneor more further polymers selected from any of the types of polymersknown in the art that are capable of being formed into fibers, includingpolyolefins, polyesters, polyamides and the like. Examples of suitablepolymers include, without limitation, polyolefins includingpolypropylene, polyethylene, polybutene, and polymethyl pentene (PMP),polyamides including nylon, such as nylon 6 and nylon 6,6,polyacrylates, polystyrenes, polyurethanes, acetal resins, polyethylenevinyl alcohol, polyesters including aromatic polyesters, such aspolyethylene terephthalate, polyethylene naphthalate, polytrimethyleneterephthalate, poly(1,4-cyclohexylene dimethylene terephthalate) (PCT),polyphenylene sulfide, thermoplastic elastomers, polyacrylonitrile,cellulose and cellulose derivatives, polyaramids, acetals,fluoropolymers, copolymers and terpolymers thereof and mixtures orblends thereof.

Further examples of aromatic polyesters include (1) polyesters ofalkylene glycols having 2-10 carbon atoms and aromatic diacids; (2)polyalkylene naphthalates, which are polyesters of2,6-naphthalenedicarboxylic acid and alkylene glycols, as for examplepolyethylene naphthalate; and (3) polyesters derived from1,4-cyclohexanedimethanol and terephthalic acid, as for examplepolycyclohexane terephthalate. Exemplary polyalkylene terephthalatesinclude without limitation, polyethylene terephthalate (also PET) andpolybutylene terephthalate.

In a preferred embodiment, the multicomponent fiber is a concentricsheath/core binder fiber with a core component (the second polymercomponent) comprising about 50% of the fiber's cross-sectional area. Thesecond polymer component can comprise semicrystalline PLA with aD-isomer content of about 2.0% or less and a corresponding melttemperature of 160° C. or higher. A sheath component (the first polymercomponent) can comprise about 50% of the fiber's cross-sectional areaand can comprise fully amorphous PLA with a D-isomer content of about 8%or more. In some embodiments, the sheath component can be blended withabout 0.5% to about 4.5% by weight of pentaerythritol prior to or duringextrusion.

Methods for making multicomponent fibers are well known and need not bedescribed here in detail. Generally, to form a multicomponent fiber, atleast two polymers are extruded separately and fed into a polymerdistribution system wherein the polymers are introduced into a segmentedspinneret plate. The polymers follow separate paths to the fiberspinneret and are combined in a spinneret hole. The spinneret isconfigured so that the extrudant has the desired shape.

Following extrusion through the die, the resulting thin fluid strands,or filaments, remain in the molten state for some distance before theyare solidified by cooling in a surrounding fluid medium, which may bechilled air blown through the strands. Once solidified, the filamentsare taken up on a godet or another take-up surface. In a continuousfilament process, the strands are taken up on a godet which draws downthe thin fluid streams in proportion to the speed of the take-up godet.In the jet process, the strands are collected in a jet, such as forexample, an air gun, and blown onto a take-up surface such as a rolleror a moving belt to form a spunbond web. In the meltblown process, airis ejected at the surface of the spinneret which serves tosimultaneously draw down and cool the thin fluid streams as they aredeposited on a take-up surface in the path of cooling air, therebyforming a fiber web. Regardless of the type of melt spinning procedurewhich is used, it is important that the thin fluid streams be melt drawndown in a molten state, i.e. before solidification occurs, to reduce thediameter of the fibers. Typical melt draw down ratios known in the artmay be utilized. Where a continuous filament or staple process isemployed, it may be desirable to draw the strands in the solid statewith conventional drawing equipment, such as, for example, sequentialgodets operating at differential speeds. See, for example, U.S. Pat. No.5,082,899, incorporated herein by reference in its entirety.

Following drawing in the solid state, the continuous filaments may becrimped or texturized and cut into a desirable fiber length, therebyproducing staple fiber. The length of the staple fibers generally rangesfrom about 25 to about 50 millimeters, although the fibers can be longeror shorter as desired. See, for example, U.S. Pat. No. 4,789,592 toTaniguchi et al, and U.S. Pat. No. 5,336,552 to Strack et al., each ofwhich is herein incorporated by reference in its entirety.

The multicomponent fibers of the invention can be staple fibers, tows,spunbond filaments, continuous filaments, or meltblown fibers. Ingeneral, staple, multi-filament, and spunbond fibers formed inaccordance with the present invention can have a fineness of about 0.5to about 100 denier. Meltblown filaments can have a fineness of about0.001 to about 10.0 denier. Monofilament fibers can have a fineness ofabout 50 to about 10,000 denier.

As noted above, the multicomponent fibers can be incorporated into anonwoven fabric. The fibers of the present invention may be formed intononwoven webs by any means suitable in the art, particularly whereinheat bonding is used. In addition, continuous filament may be spundirectly into nonwoven webs by a spunbonding process. Fibers other thanthe multicomponent fibers of the invention may be present as well,including any of the various synthetic and/or natural fibers known inthe art. Exemplary synthetic fibers include polyolefin, polyester,polyamide, acrylic, rayon, cellulose acetate, thermoplasticmulticomponent fibers (such as conventional sheath/core fibers, forexample polyethylene sheath/polyester core fibers) and the like andmixtures thereof. Exemplary natural fibers include wool, cotton, woodpulp fibers and the like and mixtures thereof.

The multicomponent fibers of the invention particularly may beincorporated, alone or in conjunction with other fibers, into ameltblown nonwoven fabric. The technique of meltblowing is known in theart and is discussed in various patents, e.g., Buntin et al., U.S. Pat.No. 3,987,185; Buntin, U.S. Pat. No. 3,972,759; and McAmish et al., U.S.Pat. No. 4,622,259, each of which is herein incorporated by reference inits entirety. Other thermal bonding means known in the art can be usedas well.

Thus, when the multicomponent fiber is subjected to an appropriatebonding temperature, at which the first polymer component is capable offorming suitable bonds, but less than the melting temperature of thesecond polymer component, the first component will soften or melt whilethe second component will generally maintain its rigid form. Themulticomponent fibers described herein are particularly suited for anair-bonding process wherein heated air (typically in the absence ofadded pressure) is used to thermally bond the fibers or a fabric formedtherewith. This includes through-air bonding and radiant-heat bonding.In various embodiments, a plurality of multicomponent fibers asdescribed herein can be air bonded at a temperature of approximately 80°C. to approximately 220° C. In a preferred embodiment, a plurality ofmulticomponent fibers as described herein can be air bonded at atemperature of approximately 130° C. Other bonding means, such ascalendar bonding or other pressure driven bonding processes for example,also can be used to form a fabric from the multicomponent fibersdescribed herein.

Nonwoven fabrics which include the multicomponent fibers of theinvention as a component are particularly suited for use in disposableproducts. Specific examples include without limitation disposablediapers, adult incontinent products, sanitary napkins, tampons, wipes,bibs, wound dressings, and surgical capes or drapes.

As discussed above, multicomponent fibers according to the presentdisclosure can be particularly beneficial in providing improved bondingcharacteristics, particularly in methods such as through air bonding.The ability to prepare a fiber per the present disclosure that performssuitably in an air bonding process can be evaluated according tomultiple different standards. As such, it is expected that one of skillin the art with the knowledge of the present disclosure can utilizepolymer components having characteristics as described herein to formmulticomponent fibers that fall within the various standards. Thefollowing description is thus provided so that one can clearly evaluatea given fiber in relation to the presently disclosed fibers and shouldnot be construed as limiting the presently disclosed fibers to onlyspecific embodiments.

One test suitable for evaluating a fiber according to the presentinvention relates to the tensile strength of a thermally bonded nonwovenweb or fabric formed using a multicomponent fiber as disclosed herein asthe sole bonding agent. Specifically, tensile strength can be evaluatedin relation to a carded nonwoven fabric comprising 75% PLA 6202D fiber(manufactured by Fiber Innovation Technology) and 25% by weight of thepresent multicomponent bonding fibers, wherein the final fabric is airbonded through a 12 second dwell time in a bonding oven at a temperatureof 130° C. An air bonded, nonwoven formed using multicomponent fibersdescribed herein as the binder fiber preferably exhibits a tensilestrength of about 500 grams force to about 4500 grams force per gram offabric weight when evaluated in the cross direction. In some embodimentsof an air bonded, nonwoven formed using multicomponent fibers describedherein as the binder fiber, the nonwoven exhibits a tensile strength ofabout 150-670 grams force for a fabric sample measuring about 1.5 inchesin length and about 2 inches in width, and having a weight of about 0.1to about 0.3 grams, when evaluated in the cross direction. One testmethod for carrying out such evaluation is described in the Example.

A further test suitable for evaluating a fiber according to the presentinvention relates to the melt flow index of one or more components ofthe fiber. Particularly, the first polymer component has a melt flowindex of about 30 or greater when evaluated according to melt flow testASTM D1238 at a temperature 210° C. and using a 2160 g basis weight. Invarious embodiments, the melt flow index of the first polymer componentis about 45 or greater, or about 60 or greater.

Yet another means for evaluating a fiber according to the presentinvention relates to the specific nature of the material used to formthe fiber. Specifically, in various embodiments the multicomponent fibercomprises a first polymer component that is fully amorphous PLA having afirst molecular weight. The multicomponent fiber further comprises asecond polymer component that is a semicrystalline PLA having a secondmolecular weight and a melt temperature of at least 150° C. In variousembodiments, the first polymer component can further comprise anadditive that can cause a reduction in the first polymer component'smolecular weight of about 5% or greater, about 10% or greater, or about15% or greater.

EXAMPLE

An exemplary, non-limiting PLA binder fiber bonding test is described,such that the sensitivity of bond strength to bonding temperature at a12 second dwell time in the bonding oven of a carded nonwoven fabriccomprising 75% PLA 6202 fibers (available from NatureWorks, LLC) and 25%experimental binder fibers can be determined. Each test sample (a cardednonwoven fabric measuring 3 inches by 2 inches, with the 2 inchdimension in the direction of carding (i.e., parallel to the fiberdirection) can be prepared as follows. First, 1.5 g of crimped PLAstaple fiber made using Natureworks grade 6202D, 2 denier per filament,1.5 inch cut length (the “matrix” fiber) can be prepared. Also, 0.5 g ofbinder fiber (as disclosed herein) can be weighed. The two fiber samplesare placed on a hand card, being careful to distribute both fibers asevenly across the card as possible. Ideally, the matrix fiber goes ontothe card first, since the experimental fiber may be uncrimped and thusis prone to falling down between the card teeth. The hand cards are usedto create a uniform blend of the two fibers. This can take severalminutes of carding, including multiple instances of removing the fibermass from the card and repositioning it before continuing with carding.Any binder fibers that are left out of the mass from falling through thecard teeth (“strays”) are retrieved, put back into the fiber mass, andblended smoothly into it. When the fiber web is uniform and thoroughlycarded, the fiber mass is removed as a single “fabric,” taking care topreserve the uniformity of the “fabric.” Using a paper template, 1.5in.×2 in. test samples are cut from the “fabric,” ensuring that theentire cut out sample has a roughly uniform fabric density and fiberdistribution throughout the sample. There can inevitably be feathery,low-density and low-uniformity edges to the fabric, so these edgespreferably are avoided and thus not included in the cut-out samples. Thesamples are oriented such that the 2 inch direction is parallel with thewidth of the card and the 1.5 inch direction is parallel with thefibers. The weight of each sample is then measured and recorded.

Once adequate samples have been prepared according to the method aboveor similar methods, the bond strength of the fibers is tested. An ovenis heated to a test temperature of 130° C., and 10 fabric samples areexposed to the test temperature for approximately 12 seconds. Due to theshort exposure time, there can be some reduction in oven temperature asa result of opening and closing the door. Therefore, the oven is allowedto regain the test temperature between sample exposures. After bonding,each sample is cooled to room temperature and then the tensile strengthis tested by pulling along a sample's 2 inch axis. This axis can be lessthan 2 inches after bonding due to shrinkage. Pulling along the fiberdirection is avoided since this will typically only test the strength ofthe fibers and not the actual bond strength. Measured tensile strengthscan be plotted against the sample's weight to normalize any varyingtenacities.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing description.Therefore, it is to be understood that the invention is not to belimited to the specific embodiments disclosed and that modifications andother embodiments are intended to be included within the scope of theappended claims. Although specific terms are employed herein, they areused in a generic and descriptive sense only and not for purposes oflimitation.

1. A multicomponent fiber having an exposed surface comprising: a firstpolymer component comprising a first aliphatic polyester, wherein thefirst polymer component forms at least a portion of the exposed surfaceof the multicomponent fiber; and a second polymer component comprising asecond aliphatic polyester; wherein about 5% or greater of the exposedsurface of the multicomponent fiber is defined by the first polymercomponent; and wherein the multicomponent fiber has a cross-sectionalarea comprising the first polymer component and the second polymercomponent in a ratio of about 1:9 to about 9:1.
 2. The multicomponentfiber of claim 1, wherein the fiber is selected from the groupconsisting of continuous filaments, staple fibers, spunbond, andmeltblown fibers.
 3. The multicomponent fiber of claim 1, wherein thefirst polymer component is polylactic acid.
 4. The multicomponent fiberof claim 1, wherein the first polymer component comprises a fullyamorphous polylactic acid having a D-isomer content of about 5% orgreater.
 5. The multicomponent fiber of claim 1, wherein the firstpolymer component comprises an additive adapted to reduce the bondingtemperature of the first polymer component, wherein the additive ispresent in an amount sufficient to reduce the bonding temperature of thefirst polymer component by about 10° C. or more.
 6. The multicomponentfiber of claim 1, wherein the first polymer component is defined by afirst molecular weight, and wherein the first polymer componentcomprises an additive in an amount sufficient to reduce the firstmolecular weight to a first reduced molecular weight.
 7. Themulticomponent fiber of claim 6, wherein the first reduced molecularweight is less than the first molecular weight by about 10% or more. 8.The multicomponent fiber of claim 6, wherein the ratio of the firstreduced molecular weight to the first molecular weight is about 0.9 orless.
 9. The multicomponent fiber of claim 9, wherein the additive isselected from the group consisting of pentaerythritol, water, sodiumhydroxide, hydrated alumina trihydrate, ethylene glycol, andcombinations thereof.
 10. The multicomponent fiber of claim 9, whereinthe first polymer component comprises about 0.5% to about 8.0% by weightof pentaerythritol.
 11. The multicomponent fiber of claim 1, wherein thefirst polymer component has a melt flow index of about 30 or greaterwhen evaluated according to melt flow test ASTM D1238 at a temperature210° C. and using a 2160 g basis weight.
 12. The multicomponent fiber ofclaim 1, wherein the second polymer component is polylactic acid. 13.The multicomponent fiber of claim 1, wherein the second polymercomponent comprises a semicrystalline polylactic acid having a D-isomercontent of about 2% or less.
 14. The multicomponent fiber of claim 1,wherein the second polymer component has a melt temperature of about160° C. or greater.
 15. The multicomponent fiber of claim 1, wherein thefirst polymer component is defined by a first molecular weight, whereinthe second polymer component is defined by a second molecular weight,and wherein the ratio of the first molecular weight to the secondmolecular weight is about 0.9 or less.
 16. The multicomponent fiber ofclaim 1, wherein the fiber exhibits a shrinkage of less than 20% afterexposure to a temperature of 130° C. for 5 minutes.
 17. Themulticomponent fiber of claim 1, wherein the fiber is adapted to imparta bonded web strength of about 150 grams force or greater for a bondednonwoven comprising the multicomponent fiber as the sole bonding agent,wherein the bonded web strength is evaluated in relation to a cardednonwoven web of 75% PLA 6202D fiber and 25% by weight of themulticomponent fiber, the web having a length of about 1.5 inches, awidth of about 2 inches, and a weight of about 0.1 to about 0.3 grams,and the web being air bonded with a 12 second residence time in abonding oven at a temperature of 130° C.
 18. A fabric comprising aplurality of thermally bonded multicomponent fibers according toclaim
 1. 19. The fabric of claim 18, wherein the fabric exhibits atensile strength of about 500 grams force or greater per gram of fabricweight
 20. The fabric of claim 18, wherein the fabric exhibits a tensilestrength of about 150 grams force or greater for a fabric sample havinga length and width of about 1.5 inches and about 2 inches, respectively,and having a weight of about 0.1 to about 0.3 grams.
 21. A method offorming a nonwoven fabric comprising: providing a plurality ofmulticomponent fibers each with an exposed surface, wherein eachmulticomponent fiber comprises a first polymer component and a secondpolymer component, and wherein the first polymer component forms atleast a portion of an exposed surface of each multicomponent fiber; andthermal air bonding the plurality of multicomponent fibers, wherein thebonding is carried out at temperature of about 80° C. to about 220° C.,and wherein the second polymer component has a melting temperature thatis greater than the bonding temperature.